Inhibition of PI-3 kinase sensitizes human leukemic cells to histone deacetylase inhibitor-mediated apoptosis through p44/42 MAP kinase inactivation and abrogation of p21CIP1/WAF1 induction rather than AKT inhibition

Abstract

Effects of the PI-3 kinase inhibitor LY294002 (LY) have been examined in relation to responses of human leukemia cells to histone deacetylase inhibitors (HDIs). Coexposure of U937 cells for 24 h to marginally toxic concentrations of LY294002 (e.g., 30 lm) and sodium butyrate (SB; 1 mm) resulted in a marked increase in mitochondrial damage (e.g., cytochrome c and Smac/DIABLO release, loss of DW m ), caspase activation, and apoptosis. Similar results were observed in Jurkat, HL-60, and K562 leukemic cells and with other HDIs (e.g., SAHA, MS-275). Exposure of cells to SB/LY was associated with Bcl-2 and Bid cleavage, XIAP and Mcl-1 downregulation, and diminished CD11b expression. While LY blocked SBmediated Akt activation, enforced expression of a constitutively active (myristolated) Akt failed to attenuate SB/LY-mediated lethality. Unexpectedly, treatment of cells with SB7LY resulted in a marked reduction in phosphorylation (activation) of p44/42 mitogen-activated protein (MAP) kinase. Moreover, enforced expression of a constitutively active MEK1 construct partially but significantly attenuated SB/LY-induced apoptosis. Lastly, cotreatment with LY blocked SB-mediated induction of p21 CIP1/WAF1 ; moreover, enforced expression of p21 CIP1/WAF1 significantly reduced SB/LY-mediated apoptosis. Together, these findings indicate that LY promotes SBmediated apoptosis through an AKT-independent process that involves MEK/MAP kinase inactivation and interference with p21 CIP1/WAF1 induction.

Potentiation of the anticancer effect of valproic acid, an antiepileptic agent with histone deacetylase inhibitory activity, by the kinase inhibitor Staurosporine or its clinically relevant analogue UCN-01

“…By itself, VA exerted a very mild growth-inhibitory effect, yet we postulated that the cytotoxic effect of VA, being an HDACI, could be enhanced by the PKC inhibitor CC or the broader spectrum kinase inhibitor STP or UCN-01. These kinase inhibitors negatively regulate PKC and ERK1/2 activation, both of which have been shown to potentiate the cytotoxic effect of HDACIs (Rahmani et al, 2003b;Maxhimer et al, 2005).…”

“…Not surprising, however, STP or UCN-01 exerted a potent inhibitory effect on PKC activity indicated by a profound time-and dosedependent depletion of p-adducin levels in treated H460 or TE12 cells. Grant and co-workers have observed reduction of MEK/ ERK1/2 activity in cells treated with combinations of HDACIs and other kinase inhibitors, including perifosine, 17-AAG or LY294002 that mediated substantial apoptosis (Dai et al, 2001;Rahmani et al, 2003bRahmani et al, , 2005. Downregulation of MEK/ERK1/2 plays an important role in the synergistic induction of apoptosis as forced expression of constitutively active MEK abrogates the cytotoxic effects of these drug combinations (Dai et al, 2001;Rahmani et al, 2003bRahmani et al, , 2005.…”

“…Grant and co-workers have observed reduction of MEK/ ERK1/2 activity in cells treated with combinations of HDACIs and other kinase inhibitors, including perifosine, 17-AAG or LY294002 that mediated substantial apoptosis (Dai et al, 2001;Rahmani et al, 2003bRahmani et al, , 2005. Downregulation of MEK/ERK1/2 plays an important role in the synergistic induction of apoptosis as forced expression of constitutively active MEK abrogates the cytotoxic effects of these drug combinations (Dai et al, 2001;Rahmani et al, 2003bRahmani et al, , 2005. It was further indicated that LY294002 enhances HDACI cytotoxicity via downregulation of MEK/ERK1/2 activity but not via abrogation of Akt activation (Rahmani et al, 2003b).…”

“…Downregulation of MEK/ERK1/2 plays an important role in the synergistic induction of apoptosis as forced expression of constitutively active MEK abrogates the cytotoxic effects of these drug combinations (Dai et al, 2001;Rahmani et al, 2003bRahmani et al, , 2005. It was further indicated that LY294002 enhances HDACI cytotoxicity via downregulation of MEK/ERK1/2 activity but not via abrogation of Akt activation (Rahmani et al, 2003b). It, therefore, appears from the literature that abrogation of MEK/ERK1/2 signalling may have more dominant impact on the enhancement of HDACI cytotoxicity in cancer cells than inhibition of Akt-mediated signalling pathway.…”

2-Methoxyestradiol-induced apoptosis in human leukemia cells proceeds through a reactive oxygen species and Akt-dependent process

“…U937 cells were stably transfected with a constitutively active form of Akt (Rahmani et al, 2005), and clones were selected with 400 mg/ml of geneticin as we have previously reported (Rahmani et al, 2003). Jurkat cells that inducibly expressing constitutively active forms of Akt have been described previously (Rahmani et al, 2003) and selected with 400 mg/ml of hygromycin.…”